1996 Polo 1600 idle fault

Has anyone got any ideas what is causing the uneven idling on my AEE powered Polo.All the usual things have been checked and checked again.The T/B has been replaced for a new one,as the ECU was originally displaying a fault code for this.The fault codes were cleared with a Bosch KTS diagnostics and the system reset.It then displayed 0 faults,but as soon as the engine reached normal operating temperature the fault reappeared,but with no fault code displayed.All vacum hoses,etc have been checked and the engine has had new plugs and air filter fitted.The intake manifold was also replaced as a precaution,as it was suggested that these can crack or split.The system has been reset 3 times by a Bosch authourised technician,but he had to admit defeat and suggested VW might be more helpful.I almost forgot to mention that the MAP sensor was also replaced,as was the Temp sensor.I am left with the probability that it may be the ECU,but several people,including the Bosch technician say this is unlikely.Any ideas would be appreciated Evil or Very Mad